Beginning in mid-September, the California Orange County Sanitation District (OCSD) will temporarily divert wastewater effluent from the main discharge pipe located 5 miles offshore (60m depth) of Los Angeles to a shorter pipe 1 mile offshore (17m depth) in order to evaluate the main pipe for maintenance. The diversion will last between 3–8 weeks. An earlier, very short diversion resulted in a bloom of potentially harmful dinoflagellates. A longer diversion will likely cause an algal bloom and, possibly, a harmful algal bloom (HAB).

Location of the OCSD long ocean outfall and short ocean outfall off Huntington Beach (Los Angeles), California (image courtesy of the OCSD)

Fortuitously, NCCOS is funding a five year, regional project in the same area to compare the effect of natural sources of nutrients versus those derived from human activities (runoff or sewage) on the development of Pseudo-nitzschia and other HAB species at “hotspots” along the California coast. Some Pseudo-nitzschia species, which occur frequently in this area, produce the potent neurotoxin domoic acid. When humans, marine mammals and marine birds consume shellfish or fish contaminated with domoic acid, they can become neurologically impaired or die. The concurrence of the ECOHAB project and the sewage diversion represents a unique opportunity to investigate the impact of large increases in nutrients derived from treated sewage on a natural ecosystem and make measurements before, during, and after a bloom. NCCOS has supported many of these researchers and agencies in a previous research project on HABs in the Southern California Bight.

Many regional scientific and management organizations will be monitoring the impact of the diversion, using an unprecedented, diverse array of new and proven technologies. NCCOS funding will be used to deploy Slocum gliders and moored Environmental Sample Processors to measure hydrographic conditions, chlorophyll, and abundance of Pseudo-nitzschia and other HABs remotely. Liquid Robotics, Inc. is providing a 2 week demonstration of instrumented wave gliders. OCSD and the Southern California Coastal Water Research Project will conduct routine water quality monitoring before and after the diversion. If a HAB occurs NCCOS-funded ships will map conditions in the outfall plume and conduct process studies to determine what is stimulating the growth of Pseudo-nitzschia or any other HABs that may develop. A National Science Foundation Rapid Response Research grant is providing pH and CO2 sensors. The Southern California Coastal Ocean Observing System (SCCOOS) website will post and provide oceanographic data during the diversion.